1. Field of the Invention
The present invention relates to a television signal transmitting and receiving system in which a television signal of a non-interlaced format is converted to television signal of an interlaced format for transmission on a transmitter side and the received signal is converted to the television signal of the non-interlaced format for picture reproduction on a receiver side.
2. Description of the Related Art
With recent significant advances in digital processing techniques for television signals, various picture quality improving methods have been proposed in the existing television broadcasting systems.
One of the methods is a picture reproducing method using non-interlaced signals which are produced by a non-interlacing type of television camera.
As described in a paper entitled "Spatial resolution of sequential scanning camera," Reports of National Convention of Television Society of Japan, pp. 41-42, 1987 (document 1), the non-interlacing television camera can significantly improve the overall resolution over existing interlacing television cameras. According to the picture reproduction method, therefore, the picture quality can be improved significantly.
As can be seen, to be compatible with the existing system, the picture reproducing method based on the non-interlaced signals requires a noninterlace-to-interlace conversion (hereinafter referred to as interlace conversion) process on the transmitter side and an interlace-to-noninterlace conversion (hereinafter referred to as noninterlace conversion) process on the receiver side.
For the interlace conversion on the transmitter side, a method in which lines are thinned out is generally used. As the noninterlace converting method on the receiver side, on the other hand, there is a converting method based on a motion-adaptive interpolation process described, for example, in "A-Motion-Adaptive High Definition Converter for NTSC Color TV Signal," SMPTE Journal, May 1984 (document 2). The converting method based on the motion adaptive interpolation process detects the motion of pictures in order to convert moving pictures in accordance with an intrafield interpolation process and convert still pictures in accordance with an interfield interpolation process.
With the converting method based on the motion adaptive interpolation process, however, since the motion of pictures is detected by detecting an interframe difference, there is a problem that reproduced horizontal edges of pictures which are abruptly switched between motion and still will flutter.
That is, with sampling clocks used for digitizing television signals, relative jitters usually occur between transmission and reception sides. Such jitters will result in false interframe difference signals at the horizontal edge portions. As a result, in detecting the movement of pictures, portions that are not moving pictures may be judged as being moving pictures. Thus, the noninterlace conversion based on the intrafield interpolation will be effected, thereby causing the reproduced edges to flutter.
Furthermore, another problem with the noninterlace conversion method is that the vertical resolution is degraded in moving areas. This is because the noninterlace conversion for moving pictures is achieved by the intrafield interpolation. If such degradation of the vertical resolution occurred with moving pictures in which an object kept still starts moving abruptly, the pictures would be blurred abruptly.
The two types of picture degradation described above become the more liable to be noticeable for an improvement in picture quality due to noninterlaced signals and thus must be solved as quickly as possible.